Zoom lens and imaging apparatus

The present disclosure relates to a zoom lens and an imaging apparatus.

In recent years, an imaging apparatus such as a digital camera has undergone an increase in size and has higher image quality. Along therewith, an imaging lens to be used for such an imaging apparatus is also required to have higher performance. Meanwhile, an optical system is also required to be miniaturized, while undergoing a shorter flange focal length by a mirrorless camera or the like. In such a background, a high-performance compact zoom lens having a wide angle of view has been proposed (PTL 1). The zoom lens proposed in PTL 1 is of a retrofocus type including a first group of negative refractive power and a rear group of positive refractive power; adopting an optimal power configuration for a short back focus allows for achievement of miniaturization. In addition, PTL 2 proposes a zoom lens similarly adopting a retrofocus type including a first group of negative refractive power, while having a high variable magnification ratio in which a focal distance on a side of a telephoto end is expanded.

As for a zoom lens proposed in PTL 1, a compact and high-performance zoom lens having a wide angle of view range is provided, but a variable magnification ratio thereof is insufficient. In addition, a zoom lens proposed in PTL 2 achieves a high variable magnification ratio while adopting a configuration of a retrofocus type similar to that of PTL 1, but has a longer total length and a larger diameter of a first group, resulting in insufficient miniaturization.

It is desirable to provide a compact and high-performance zoom lens having a high variable magnification ratio as well as an imaging apparatus including such a zoom lens.

A zoom lens according to an embodiment of the present disclosure includes a plurality of lens groups including, in order from a side of an object toward a side of an image plane, a first lens group including two or less lenses and having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, a fourth lens group having positive refractive power, and a fifth lens group having negative refractive power. Upon zooming from a wide-angle end to a telephoto end, at least the first lens group, the third lens group, and the fourth lens group are configured to move to the side of the object. The following conditional expressions are satisfied:

An imaging apparatus according to an embodiment of the present disclosure includes a zoom lens and an imaging element that outputs an imaging signal corresponding to an optical image formed by the zoom lens, and the zoom lens is configured by the zoom lens according to an embodiment of the present disclosure.

In the zoom lens or the imaging apparatus according to an embodiment of the present disclosure, the configuration of each of the lens groups is optimized to enable achievement of compactness, high performance, and a high variable magnification ratio.

Hereinafter, description is given in detail of embodiments of the present disclosure with reference to the drawings. It is to be noted that the description is given in the following order.

An embodiment of the present disclosure relates to a zoom lens suitable for a digital still camera, a digital mirrorless camera, or the like, and to an optical apparatus including such a zoom lens. In particular, an embodiment of the present disclosure relates to a miniaturized and lightweight imaging lens having high performance throughout the entire zoom range to which a group configuration and a zooming trajectory enabling a favorable aberration correction are applied, as well as to an imaging apparatus including such an imaging lens.

illustrates a first configuration example of a zoom lens according to an embodiment of the present disclosure, and corresponds to a configuration of Example 1 described later.illustrates a second configuration example of the zoom lens according to an embodiment, and corresponds to a configuration of Example 2 described later.illustrates a third configuration example of the zoom lens according to an embodiment, and corresponds to a configuration of Example 3 described later.illustrates a fourth configuration example of the zoom lens according to an embodiment, and corresponds to a configuration of Example 4 described later.illustrates a fifth configuration example of the zoom lens according to an embodiment, and corresponds to a configuration of Example 5 described later.illustrates a sixth configuration example of the zoom lens according to an embodiment, and corresponds to a configuration of Example 6 described later.illustrates a seventh configuration example of the zoom lens according to an embodiment, and corresponds to a configuration of Example 7 described later.illustrates an eighth configuration example of the zoom lens according to an embodiment, and corresponds to a configuration of Example 8 described later.illustrates a ninth configuration example of the zoom lens according to an embodiment, and corresponds to a configuration of Example 9 described later.illustrates a tenth configuration example of the zoom lens according to an embodiment, and corresponds to a configuration of Example 10 described later.illustrates an eleventh configuration example of the zoom lens according to an embodiment, and corresponds to a configuration of Example 11 described later.illustrates a twelfth configuration example of the zoom lens according to an embodiment, and corresponds to a configuration of Example 12 described later.illustrates a thirteenth configuration example of the zoom lens according to an embodiment, and corresponds to a configuration of Example 13 described later.

Inand other drawings, Zdenotes an optical axis. An optical member such as a cover glass for protecting an imaging element may be disposed between an image plane IMG and any of zoom lensestoaccording to the first to thirteenth configuration examples. Further, in addition to the cover glass, various optical filters such as a low-pass filter or an infrared cut filter may be disposed as the optical member.

Hereinafter, description is given of a configuration of the zoom lens according to an embodiment of the present disclosure, as appropriate, in association with the zoom lensestoaccording to the respective configuration examples illustrated inand other drawings. However, the technique according to the present disclosure is not limited to the illustrated configuration examples.

The zoom lens according to an embodiment includes a plurality of lens groups. The plurality of lens groups includes, in order from an object side toward an image plane side, a first lens group Ghaving positive refractive power, a second lens group Ghaving negative refractive power, a third lens group Ghaving positive refractive power, a fourth lens group Ghaving positive refractive power, and a fifth lens group Ghaving negative refractive power. The first lens group Gis configured by two or less lenses.

Here, in the zoom lens according to an embodiment, the “lens group” refers to a lens group having refractive power and having an interval that varies with respect to an adjacent lens group upon zooming. A lens group configured only by a flat plate having no refractive power is not defined as the lens group.

In the Examples described later, the zoom lensestoandtoaccording to Examples 1 to 8 and 10 to 13 include the first lens group Gto the sixth lens group as the plurality of lens groups. The zoom lensaccording to Example 9 includes the first lens group Gto the fifth lens group Gas the plurality of lens groups.

The zoom lens according to an embodiment is configured to allow at least the first lens group G, the third lens group G, and the fourth lens group Gto move to the object side upon zooming from a wide-angle end to a telephoto end. It is to be noted that, inand other drawings, a lens arrangement upon infinity focusing at a wide-angle end (Wide) is illustrated at the upper part, and a lens arrangement upon infinity focusing at an intermediate position (Mid) is illustrated in the middle part. In addition, a lens arrangement upon infinity focusing at the telephoto end (Tele) is illustrated in the lower part.

In addition to those described above, the zoom lens according to an embodiment may further satisfy a predetermined conditional expression or the like described later.

Next, description is given of workings and effects of the zoom lens according to an embodiment of the present disclosure. In addition thereto, description is given of a more preferable configuration in the zoom lens according to an embodiment of the present disclosure as well as of the workings and effects thereof.

It is to be noted that the effects described in herein are merely exemplary and are not limited thereto, and may further include other effects.

According to the zoom lens according to an embodiment, configurations of the respective lens groups are optimized to enable achievement of compactness, high performance, and a high variable magnification ratio. This makes it possible to provide a compact and high-performance zoom lens having a high variable magnification ratio as well as an imaging apparatus including such a zoom lens.

The zoom lens according to an embodiment includes, in order from the object side toward the image plane side, the first lens group Ghaving positive refractive power, the second lens group Ghaving negative refractive power, the third lens group Ghaving positive refractive power, the fourth lens group Ghaving positive refractive power, and the fifth lens group Ghaving negative refractive power. The zoom lens according to an embodiment is configured to allow at least the first lens group G, the third lens group G, and the fourth lens group Gto move to the object side upon the zooming from the wide-angle end to the telephoto end. Upon the zooming, movement trajectories (movement amounts) of the first lens group G, the third lens group G, and the fourth lens group Gmay differ from one another. This increases flexibility of the movement trajectory of a zoom variator, thus making it possible to secure high optical performance throughout the entire zoom range while earning the variable magnification ratio. In addition, setting the first lens group Gto be a lens group having positive refractive power and configuring the first lens group Gby two or less lenses suppress an increase in size of the first lens group G, thus making it possible to reduce the size and weight of the optical system.

The zoom lens according to an embodiment may satisfy the following conditional expression (1):

The conditional expression (1) is defined to achieve a wider angle of the optical system and higher performance thereof, and is a conditional expression to appropriately set the focal distance of the second lens group Gwith respect to the focal distance of the first lens group G. Exceeding an upper limit value of the conditional expression (1) increases the positive refractive power of the first lens group G, thus making it difficult to correct various aberrations generated in the first lens group G. In addition, the negative refractive power of the second lens group Gis decreased, thus making it difficult to achieve the wider angle.

It is to be noted that the upper limit value of the conditional expression (1) may be set to −6.50 or even to −6.80. This makes it possible to further suppress the various aberrations generated in the first lens group G. In addition, securing the negative refractive power of the second lens group Gfacilitates the wider angle of the optical system more advantageously. In addition, decreasing the value of the conditional expression (1) intensifies the negative refractive power of the second lens group G, thus making it difficult to correct various aberrations. Therefore, the lower limit value of the conditional expression (1) may be set to −15.00 or even to −13.0, from the viewpoint of higher performance of the optical system.

In addition, the zoom lens according to an embodiment may satisfy the following conditional expression (2):

The conditional expression (2) is defined to achieve a higher variable magnification ratio of the optical system and higher performance thereof, and is a conditional expression to appropriately set the focal distance of the fourth lens group Gwith respect to the focal distance of the third lens group G. Exceeding an upper limit value of the conditional expression (2) increases the positive refractive power of the fourth lens group G, thus making it difficult to correct spherical aberration and coma aberration generated in the fourth lens group G. Meanwhile, falling below a lower limit value of the conditional expression (2) reduces the positive refractive power of the fourth lens group G, thus reducing a change in a focal distance of the entire optical system due to a change in an interval between the third lens group Gand the fourth lens group G. This makes it difficult to achieve the higher variable magnification ratio.

It is to be noted that the upper limit value of the conditional expression (2) may be set to 4.00 or even to 3.8. This makes it possible to further suppress the spherical aberration and the coma aberration generated in the fourth lens group G. In addition, the lower limit value of the conditional expression (2) may be set to 1.80 or even to 1.85, from the viewpoint of higher variable magnification ratio of the optical system.

In addition, the zoom lens according to an embodiment may satisfy the following conditional expression (3):

The conditional expression (3) is defined to achieve miniaturization of the optical system and a wider angle of the optical system, and is a conditional expression to appropriately set a focal distance of the total system at the wide-angle end with respect to the focal distance of the first lens group G. Exceeding an upper limit value of the conditional expression (3) reduces the positive refractive power of the first lens group G, thus increasing the movement amount of the first lens group Gat the time of varying the magnification. This makes it difficult to miniaturize the optical system. Meanwhile, falling below a lower limit value of the conditional expression (3) increases the focal distance of the total system at the wide-angle end, thus resulting in an insufficient wider angle of the optical system.

It is to be noted that the upper limit value of the conditional expression (3) may be set to 13.0 or even to 10.0, from the viewpoint of miniaturization of the optical system. In addition, the Lower limit value of the conditional expression (3) may be set to 6.0 or even to 6.3. This makes it possible to achieve a still wider angle of the optical system.

In addition, the zoom lens according to an embodiment may satisfy the following conditional expression (4):

The conditional expression (4) is defined to allow the optical system to have a more telephoto property and to suppress aberration of the optical system, and is a conditional expression to appropriately set the focal distance of the total system at the telephoto end with respect to the focal distance of the fourth lens group G. Exceeding an upper limit value of the conditional expression (4) reduces the focal distance of the total system at the telephoto end too much, thus resulting in an insufficient telephoto property of the optical system. Meanwhile, falling below a lower limit value of the conditional expression (4) increases the positive refractive power of the fourth lens group Gtoo much, thus makes it difficult to correct the spherical aberration and the coma aberration generated in the fourth lens group G.

It is to be noted that the upper limit value of the conditional expression (4) may be set to 0.50 or even to 0.45, from the viewpoint of the telephoto property of the optical system. This enables the optical system to have a more telephoto property. In addition, the lower limit value of the conditional expression (4) may be set to 0.20 or even to 0.25. This makes it possible to further suppress the spherical aberration and the coma aberration generated in the fourth lens group G.

In addition, the zoom lens according to an embodiment may be configured to allow the fifth lens group Gto move as a focusing lens group in an optical axis direction and thereby perform focusing, when an object distance varies from infinity to a short distance. Inand other drawings, an arrow indicates a moving direction of the focusing lens group upon focusing from infinity to a short distance.

In recent years, a reduction in a variation of an angle of view at the time of focusing has been strongly demanded in the field of moving images, or the like. To meet that demand, the focusing lens group may be disposed at a position close to the image plane IMG. In addition, in the zoom lens according to an embodiment, it is preferable to secure moving distances of the third lens group Gand the fourth lens group Gas long as possible, as the zoom variator, upon zooming from the wide-angle end to the telephoto end. In a case where the third lens group Gor the fourth lens group Gis set as the focus lens group, it is necessary to additionally secure the movement amount thereof by the focusing in the optical axis direction, thus leading to an increase in the size of the optical system. Accordingly, it is sufficient for the fifth lens group Gto be set as a focusing group in the zoom lens according to an embodiment, from the viewpoint of reducing the variation of the angle of view upon the focusing and the miniaturization of the optical system.

In addition, the zoom lens according to an embodiment may include an aperture stop St between the second lens group Gand the third lens group G.

In the zoom lens according to an embodiment, in a case where the aperture stop St is disposed in the second lens group Gor on a side closer to an object than the second lens group G, the number of lenses disposed on the side closer to the object than the aperture stop St is reduced, thus making it difficult to correct distortion and appropriately correct upper and lower beams of an off-axis light beam. This makes it difficult to suppress various aberrations, which is not preferable from the viewpoint of higher performance of the optical system. Meanwhile, in a case where the aperture stop St is disposed in the third lens group Gor on a side closer to an image plane than the third lens group G, a diameter of the off-axis light beam passing through the first lens group Gand the second lens group Gis increased, thus making it difficult to reduce a diameter of the first lens group G. In addition, an on-axis light beam is incident on the third lens group Gand the fourth lens group Gin a state of being diffused by the second lens group G, thus causing the stop mechanism to have a larger size, which is not preferable for miniaturization of the entire optical system. It is therefore desirable to provide the aperture stop St between the second lens group Gand the third lens group G, from the viewpoint of suppressing various aberrations and miniaturization of the optical system.

In addition, the zoom lens according to an embodiment may be configured to allow the third lens group Gand a final lens group GR in the plurality of lens groups to move in the same trajectory upon zooming from the wide-angle end to the telephoto end. It is to be noted that, in Examples described later, the zoom lensestoandtoin Examples 1 to 8 and 10 to 13 correspond to this configuration; the third lens group Gand a sixth lens group Gas the final lens group GR move in the same trajectory.

In the zoom lens according to an embodiment, in a case where the final lens group GR does not move in the optical axis direction upon zooming from the wide-angle end to the telephoto end, a height of the off-axis light beam to be incident on the final lens group GR at the telephoto end is increased, which is disadvantageous in reduction in the size and the weight. Meanwhile, in a case where the final lens group GR independently moves in the optical axis direction upon zooming from the wide-angle end to the telephoto end, the number of movable lens groups upon zooming is increased, thus causing a mechanical configuration for zooming to be complicated, which is not preferable from the viewpoint of miniaturization and construction of the mechanical configuration. It is therefore desirable for the third lens group Gand the final lens group GR to move in the same trajectory upon zooming from the wide-angle end to the telephoto end, from the viewpoint of the miniaturization and the construction of the mechanical configuration.

In addition, in the zoom lens according to an embodiment, the fourth lens group Gmay have an aspherical surface and include a positive lens PLthat satisfies the following conditional expressions (5) and (6). It is to be noted that, in Examples described later, a lens Lcorresponds to the positive lens PL, in the zoom lensesto,to, andaccording to Examples 1 to 4, 6 to 8, and 13. In addition, in the zoom lensestoaccording to Examples 9 to 11, a lens Lcorresponds to the positive lens PL. In addition, in the zoom lensaccording to Example 12, a lens Lcorresponds to the positive lens PL.

In the zoom lens according to an embodiment, a light beam is diffused by negative refractive power in the second lens group G, thus causing a height of the on-axis light beam to be incident on the fourth lens group Gis increased. In addition, the fourth lens group Gserves the role of a variator upon zooming from the wide-angle end to the telephoto end, and desirably has stronger positive refractive power for higher variable magnification. In this case, it becomes difficult to correct aberration in the fourth lens group G. It is therefore desirable for the fourth lens group Gto have an aspherical surface for the correction of aberration.

The conditional expression (5) is defined to secure workability of a lens and to suppress chromatic aberration, and is a conditional expression to appropriately set Abbe number of the positive lens PL. Exceeding an upper limit value of the conditional expression (5) increases a difficulty level of forming a material of the lens, thus making it difficult to ensure the manufacturability. Falling below a lower limit value of the conditional expression (5) makes it difficult to correct axial chromatic aberration and off-axis chromatic aberration generated in the positive lens PL.

It is to be noted that the upper limit value of the conditional expression (5) may be set to 95.0 or even to 85.0, from the viewpoint of the manufacturability of the lens. In addition, the lower limit value of the conditional expression (5) may be set to 65.0 or even to 70.0. This makes it possible to further suppress the axial chromatic aberration and the off-axis chromatic aberration generated by the positive lens PL.